CHEM 103 Exam 2 Ultimate Combined

Valence Electrons

Electrons in the highest occupied energy level (n level). S & P sublevels. Up to 8. Group number = number of valence lectrons.

Lewis Dot Symbols

Represent valence electrons as dots around atomic symbol. (1-4 valence electrons = single dots; 5-8. valence electrons = pairs of dots).

The Octet Rule

An atom is stabilized by having its valence energy level filled.

Noble gases fulfill the octet rule. Other atoms fulfill the octet rule by: Gaining/losing electrons (Ionic compounds) or Sharing electrons (Covalent compounds).

How do atoms other than noble gases fulfill the octet rule?

By Gaining/losing electrons (Ionic compounds) or Sharing electrons (Covalent compounds).

Ions

Atoms or groups of atoms that have an overall charge. Charges are superscript.

Ag Ion Charge

1+.

Zn Ion Charge

2+.

Cd Ion Charge

2+.

Cations

Positively charged ions. Main group metals fulfill the octet rule by forming Cations. (Losing electrons).

Naming Cations

Metal cations have the same name as the neutral metal (i.e. Na+ = Sodium).

Metals with variable charges: Use Roman numerals to indicate the charge (i.e. Fe²⁺ = iron (II)).

Name the following cations:

Ag+, Pb2+, Pb4+

Silver, Lead(II), Lead(IV).

Anions

Negatively charged ions. Most nonmetals fulfill the octet rule by gaining electrons.1

Naming Anions

Change ending to -ide. (i.e. Cl- = Chloride).

Polyatomic Ions

Groups of atoms with a charge.

Oxyanions

Contain oxygen (and another element). (i.e. CO3²⁻, or PO4³⁻).

Ionic Charge Trends

Group 1A: 1+.

Group 2A: 2+.

Group 3A: 3+ (only for Al).

Ag+, Cd2+, Zn2+.

Group 5A: 3-.

Group 6A: 2-.

Group 7A: 1-.

Ionic Bond

Attraction between oppositely charged ions. (Metals, Polyatomics)

Ionic Compound

- Oppositely charged ions (Between Metals & Nonmetals, or including Polyatomics ions).

- Do NOT form molecules.

- Formula unit or empirical unit.

- May use roman numeral.

Ionic Bond vs. Ionic Compound

Ionic Bond: Attraction between oppositely charged ions.

Ionic Compound: Opposite ions forming a compound, consists of a + & - charge.

Ionic Bond Compound Notation Rules

- Cation listed first, then Anion listed second.

- Subscripts tell how many of each atom.

- Subscripts are placed after the atom they are used for.

- Parenthesis are used when there are multiple of the SAME polyatomic ion.

- Ionic bonds occur between oppositely charged ions.

- In ionic compounds, total charge = 0.

Ionic Lattice

An array of positive & negative ions.

Chemical Formulas

Show the type and amount of each element present.

Empirical Formula

The smallest whole-number ratio of atoms (always used for ionic compounds).

Formula Unit

The smallest number of ions necessary to form a compound.

Empirical Formula vs. Formula Unit

Empirical Formula: The smallest whole-number ratio of atoms (always used for ionic compounds).

Formula Unit: The smallest number of ions necessary to form a compound.

Write the formula for a compound composed of potassium and sulfide ions

K2S

Write the formula for a compound composed of Mn4+ and O^2-

MnO2

Write a formula for a compound composed of calcium and carbonate ions

CaCO3

Write the formula for a compound composed of aluminum and sulfate ions

Al2(SO4)3

Write the formula for ammonium sulfide

(NH4)2S

Name the compound Fe(NO2)2

Iron (II) Nitrite

Covalent Bond

Valence electrons shared between 2 atoms. Fulfill the octet rule by sharing electrons.

The 7 Elements that Form Diatomic Molecules

H2, N2, F2, O2, I2, Cl2, Br2. (Have No Fear Of Ice Cold Beer).

Have No Fear Of Ice Cold Beer

H2, N2, F2, O2, I2, Cl2, Br2 (How to remember the 7 elements that form diatomic molecules).

Double Covalent Bond

Shares 2 pairs of electrons.

Triple Covalent Bond

Shared 3 pairs of electrons.

Bonding Electrons vs. Nonbonding Electrons

Bonding Electrons: Electrons in bonds, usually signified by N-N, N=N, etc.

Nonbonding Electrons (lone pairs): Unshared electrons that are not in bonds, usually signified as the dots (i.e. :H=H:).

Naming Binary Covalent Compounds: Prefixes (1-10)

1: Mono- (omit for first element).

2: Di-

3: Tri-

4: Tetra-

5: Penta-

6: Hexa-

7: Hepta-

8: Octa-

9: Nona-

10: Deca-

Name these compounds: PCl3 & PCl5

Phosphorus Trichloride & Phosphorus Pentachloride.

Nitrogen and oxygen form 2 covalent compounds, NO2 and N2O4. Name each of these compounds.

Nitrogen Dioxide and Dinitrogen Tetroxide.

Do you simplify Ionic Compound and/or Covalent Compound formulas?

You simplify Ionic Compounds to their empirical formula, but you do NOT simplify Covalent Compound formula.

Ionic Compounds vs. Covalent Compounds

Ionic Compounds: Oppositely charged ions (Between Metals & Nonmetals, or including Polyatomics ions). Do NOT form molecules. Formula unit or empirical unit. May use Roman Numeral.

Covalent Compounds: Share electrons. Between nonmetal atoms (or B & Si). Usually form molecules. Molecular formula. Uses prefixes.

Covalent Compound

- Share electrons.

- Between nonmetal atoms (or B & Si).

- Usually form molecules.

- Molecular formula.

- Use prefixes.

Identify these compounds as ionic or covalent, and name each one:

MgF2

P2O4

Fe(NO3)3

SCl6

Ionic: MgF2 & Fe(NO3)3.

Covalent: P2O4 & SCl6.

MgF2: Magnesium Fluoride.

P2O4: Diphosphorus Tetroxide.

Fe(NO3)3: Iron (III) Nitrate.

SCl6: Sulfur Hexachloride.

Aqueous Solution

Homogenous mixture where the main component is water (solvent).

Soluble

Able to dissolve in water.

Dissociation

Ions are pulled apart in an aqueous solution. (i.e. NaCl -> Na+ + Cl-). (Only for ionic compounds, covalent molecules do not dissociate).

Do Ionic Compounds and/or Covalent Molecules Dissociate?

Ionic do, Covalent do not.

(Because it is about ions being pulled apart, so only ionic is capable of that).

Reactant vs. Product

Reactant are the beginning of a chemical reaction and Products are what result from the reaction.

Balanced Equation (and Strategies)

When the number and type of each atom are the same on both sides of the arrow.

Strategies: Balance solo elements last, start with the compounds. Balance polyatomic ions as units when present on both sides of the equation. Use a fractional coefficient when needed, but decimal coefficients are NOT allowed.

How to do Fractional Coefficient in Balancing Equations

Total on the right / subscript on left. (i.e. 7/2)

Phase Notations

Show phase or state of reaction components. (s) means Solid, (l) means Liquid, (g) means Gas, & (aq) means Aqueous solution (dissolved in water).

(aq)

Indicates the substance is dissolved in water.

Decomposition Reaction

One forms two or more.

Synthesis (Combination) Reaction

Two form one.

Single Displacement Reaction

One element replaces another.

(A compound reacts with an element to make a new compound and a new element).

Double Displacement Reaction

Two ions replace each other.

(2 compounds react to form 2 new compounds).

Metal + Nonmetal ->

Ionic Compound (has charge)

Oxidation

Loss of electrons (charge goes up)(+).

Reduction

Gain of electrons (charge goes down)(-).

Ionic Compound vs. the Metal + Nonmetal

Ionic Compound has charge, whereas the Metal and Nonmetal are neutral.

How do we know what is oxidized and reduced?

- Look at charges.

- Compounds follow our charge rules for ionic compounds.

- Pure elements (including the diatomics) are net neutral.

Reactions between Metals and Nonmetals Examples

What is being Oxidized and Reduced?

Ca (s) + S (s) -> CaS (s)

Mg (s) + Cl2 (g) -> MgCl2 (s)

2Fe2O3 -> 3O2 + 4Fe

Ca was oxidized, S was reduced.

Mg was oxidized, Cl was reduced.

O was oxidized, Fe was reduced.

Combustion Reactions

Reactions in which oxygen gas combines with elements or compounds to produce oxides. (i.e. Sn + O2 -> SnO2).

Hydrocarbons

Compounds composed of hydrogen and carbon.

Combustion of Hydrocarbons

Hydrocarbon + oxygen -> carbon dioxide + water.

# C#H# + # O2 -> # CO2 + # H2O.

Write a balanced equation for the combustion of calcium metal

2Ca + O2 -> 2CaO.

Write a balanced equation for the combustion of propane gas, C3H8. Then do it for C9H20.

C3H8 + 5 O2 -> 3 CO2 + 4 H2O.

C9H20 + 15 O2 -> 9 CO2 + 10 H2O.

Ionic compounds ________ when dissolved in water.

Dissociate.

Molecular Equation

Shows ions together as only compounds. KBr (s) -> KBr (aq).

Ionic Equation

Shows dissociated ions as separate species. KBr (s) -> K+ (aq) + Br- (aq).

Show this process as an ionic equation (dissociation equation)

Mg(NO3)2 (s) -> Mg(NO3)2 (aq)

Mg(NO3)2 (s) -> Mg^2+ + 2 NO3^- (aq)

Molecular Equation vs. Ionic Equation

Molecular Equation: Shows ions together as only compounds. KBr (s) -> KBr (aq).

Ionic Equation: Shows dissociated ions as separate species. KBr (s) -> K+ (aq) + Br- (aq).

Soluble ionic compounds ________ in water. Some ionic compounds are _______ in water.

Dissociate; Insoluble.

Compounds that are soluble in water are

More stable in the solvated state than as a solid. (Lower energy = more stable).

Factors affecting solubility

- Charge on ions.

- Size of ions.

- How tightly the ions are packed together.

Halogens: Solubility Rules

Halogens (F-, Br-, Cl-, I-) are soluble. Unless bonded to Ag+ or Pb2+.

Precipitation Reaction

2 aqueous (aq) solutions that when mixed, produce an insoluble product (s).

Precipitate

The solid product that is formed.

Driving force for Precipitation Reaction

To form the solid, which is more stable than the ions in solution.

Molecular Equation vs. Complete Ionic Equation vs. Net Ionic Equation

Molecular Equation: Shows neutral compounds.

Balanced equation that has all the normal stuff.

Complete Ionic Equation: Shows all ions present.

All (aq) are broken into ions, but solid stays together. Bring subscripts out in front as coefficients. Multiply by the coefficients from the molecular equation.

Net Ionic Equation: Omits spectator ions; only shows ions that react.

Only contains the ions to make the solid. Others are "spectator ions".

Complete Ionic Equation

- All (aq) are broken into ions, but solid stays together.

- Bring subscripts out in front as coefficients.

- Multiply by the coefficients from the molecular equation.

Net Ionic Equation

Only contains the ions to make the solid. Others are "spectator ions".

Spectator Ions

Ions that do not take part in the reaction that is making the solid.

Steps to Completing Double Displacement Reactions

Step 1: Break the reactants into their respective ions.

Step 2: Swap the cations.

Step 3: Criss-Cross to form the product compounds.

Step 4: Balance the equation.

Boom, now you have molecular formula, then you can go through complete ionic equation, then net ionic equation when necessary.

Formula Mass

The mass of a single molecule (covalent) or formula unit (ionic compound). (i.e. Formula Mass of a water molecule, H2O is 2(1.008) + 1(16.00) = 18.016 u). Do not round.

Formula Mass of the compound K2CO3

138.21 u.

Percent Composition

Percent composition of one element = mass of one element / mass of compound x 100%.

Molecular Formula C8H18. Determine Percent Composition of Carbon and Hydrogen.

Carbon: 84.09%

Hydrogen: 15.91%

Mass Spectrometry

A technique used to measure the mass of molecules.

Elemental Analysis

A technique used to measure percent composition. Uses combustion reactions to form simpler products (CO2, H2O).

Avogadro's Number

6.02 x 10^23 particles of atom/molecule (which is equal to 1 mol of atom/molecule).

Formula Mass & Molar Mass of Carbon Dioxide

1 molecule of CO2 = 44.01 u.

1 mol CO2 = 44.01 g.

Molar Ratio

ANY 2 components can be related through the molar ratio of a balanced reaction.

Example: CH4 + 2 O2 -> CO2 + 2 H2O

Can do Reactant:Reactant, Reactant:Product, or Product:Product.

So, examples: 1 mol CH4 = 2 mol O2. 1 mol CH4 = 1 mol CO2. 1 mol CO2 = 2 mol H2O.

Stoichiometry

Using the amount of one material to predict the amount of another, based on the balanced equation.

Molar Ratio is always

Exact.

Grams A <-> Moles A

Use Molar Mass.

Moles A <-> Particles A

Use Avogadro's Number.

Moles A <-> Moles B

Use Molar Ratio from the balanced equation.

Limiting Reagent

Completely consumed; limits the amount of product formed. The reagent that forms the least amount of product is the limiting reagent.